Currently there is no way to embed Blend4Web in a Facebook post, the only option available is creating a Facebook Canvas app. This is because we do not have a Blend4Web-specific hosting service. Our current business model does not rely on any web services which I believe is our advantage over cloud-based platforms notoriously known for their customer lock-in and privacy violations. You are free to choose any third-party hosting platform or use your own or your customer's website for displaying Blend4Web content.